With traditional electronic flash systems such as Xenon flash tubes, prevalent in photography since the 1950's, users have been forced to preview images using tungsten modelling lamps as constant light which are 3200 k as opposed to the colour temperature of the flash (5000-5500 k). In addition to this issue regarding colour balance, for many years the industry struggles with ways to configure the orientation of the Xenon flash tube and the tungsten modelling light. This results in a sometimes dramatic difference in the character of light between the flash and the preview. This is relevant in for example photography for museum conservation, forensic photography, product photography, portrait photography, etc. Essentially, any application where the previewing of a scene needs to be colour critical or equal in character is relevant.
Early image capturing, especially in photography, relied on daylight for exposure due to the low sensitivity of the early photographic materials. As the technology matured tungsten lighting became prevalent. Electronic flash systems slowly became prevalent in photography since the 1950's and by the 1970's became the mainstream choice for colour photography. The primary benefit of electronic flash systems is the fact that a large quantity of light is released in a shorter time window compared to tungsten lighting (generally 1/400th sec to 1/10000th sec). This short duration capability allowed the photographer to freeze action such as a model's hair or glass breaking in extreme examples. However, more powerful electronic flash systems used in studios have a large time window and are therefore slower compared to low powered electronic flash systems found in for example cell phones. Electronic flash systems used in high-end studio flashes have the drawback that they have a relative large time window and limit the creative possibilities in image capturing.
With traditional electronic flash lighting solutions there is very little control of the Xenon flash event, and in most cases the light output ramps up and peaks to full power, then decades in a fixed pattern that cannot be controlled by the user. Traditional electronic flash systems have as drawback that they have relatively unpredictable characteristics and limit the creative possibilities of image capturing.
Electronic flash systems generally incorporate fragile and expensive glass tubes. Tungsten modelling lamps do not travel well and are prone to breakage. Also light forming accessories for electronic flash systems need to stand up to very high temperature due to 125 to 250 Watt tungsten modelling lamps and electronic flash systems comprising high energy density glass tubes. A drawback of state of art lighting equipment for image capturing is that the accessories are heavy and unsafe to handle.
With the advent of digital photography the use of solid state imaging systems such as CCD CMOS, the line between still image capturing and moving image capturing such as (HD) video capturing has been blurred. Several digital still image cameras employ both still and moving image capturing modes, and conversely many moving image cameras incorporate a still image capturing capability. It is a drawback that moving image capturing requires constant lighting, and for still image capturing, electronic flash systems have been the predominant technology.
Almost all traditional photographic light sources emit amounts of UV and infrared light spectrum. This has as drawback that the IR and UV light can damage certain frequency sensitive objects while capturing its image using flash. For example, this can be the case when photographing extremely rare documents or art works.
A viewing system is used to compare image prints or originals with the image displayed on a monitor. During such comparing, digital image users evaluate colour results. These viewing systems are usually 5000 k following ISO standard viewing conditions traditionally based on fluorescent tubes and have a colour rendering of about 85 to 95 CRI. A drawback of these viewing systems is that the spectrum emitted by the fluorescent tubes has distinct spikes, which accentuate the effect of metamerism. Metamerism is the matching of apparent colour of objects with different spectral power distributions. The negative effect of metamarism occurs in situations where two image samples match when viewed under one light source but do not match under another. Most types of fluorescent lights produce an irregular or peaky spectral emission curve, so that two image samples under fluorescent light might not match, even though they are a metameric match to an incandescent “white” light source with a nearly flat or smooth emission curve. Image sample colours that match, viewed under one source will often appear different under the other. Obviously, this is a further drawback in the image capturing process as evaluating colour results with conventional viewing systems is arbitrary.
It is well-known that lighting equipment in image capturing, especially in the high-end market, has as drawback that they are heavy in terms of weight. Large power supply units (usually referred to as “generators” or “power packs”) are needed to supply tungsten lamps and/or electronics flash systems of sufficient energy to produce the high quality and high brightness lighting.
It is also a drawback that the recycle time (the time it takes for electronic flash systems to store and release energy) can be quite long. For example: a typical digital SLR system may be able to capture five images per second, but even the best studio electronic flash systems require one to four seconds between exposures at full power. This is a drawback for any number of photographic applications especially fashion, portraiture, sports, events, and any other type of photography where the camera capture rate needs to be responsive to the event being captured.
It is also well known that moving image capturing, such as motion picture and video imaging are based upon capturing a series of still images at fixed frequencies. This is also known as shutter speed and is expressed in frames per second (fps). Common shutter speeds are 24 fps or 30 fps. An alternative way to express the frequency of capturing the series of still images is the use of shutter time or exposure time, which defines a start of capturing a still image and an end of capturing the still image. Current lighting technologies include HMI, Tungsten modelling lamps, HF fluorescent, HID and electronic flash systems. A drawback of these systems is that they lead to expensive post-production and other colour corrections.
When capturing a specific frequency spectrum spectral cut filters are placed before dedicated camera lenses. This type of spectral imaging has benefits in for example when used in museums, medical, or law enforcement applications. In these cases specific spectral frequencies are filtered to highlight specific items such as a certain paint pigment, skin discolorations, blood stains or fingerprints. In digital imaging applications, multiple colour channels can be combined to create highly colour accurate images. Often this is accomplished using monochromatic CCD or CMOS sensors, but multi-spectral imaging can also be applied to common RGB type sensors. It is a drawback that colour CCD, CMOS and other sensor technologies have different spectral sensitivities as colour filter arrays are affixed to the monochromatic sensor or in the optical path. Light with frequencies within and beyond the visible spectrum are not effectively utilised for exposure and in fact, unwanted wavelengths of ultraviolet and infrared frequencies have to be blocked with additional filtration.
The known lighting system has the drawback that when utilised for (digital) image capturing (still image or motion image capturing) light not visible to a still or motion camera is not effectively utilised.
The known lighting system used in image capturing has the drawback that the resulting image does not always resemble the preview image limiting the possibilities of image capturers.
It is an object of the invention to at least partially eliminate the abovementioned drawback or to at least provide a usable alternative. In particular, it is an object of the present invention to provide an improved lighting system that allows for more accurate image capturing.